From 72c2051a10107d8b75d6ec59dd490119b63ff9ff Mon Sep 17 00:00:00 2001
From: Titus Wormer <tituswormer@gmail.com>
Date: Tue, 17 Sep 2024 12:35:40 +0200
Subject: [PATCH] rehype-remove-comments: add support for `test`

Closes GH-50.
---
 packages/hast-util-from-string/lib/index.js  |  2 +-
 packages/rehype-remove-comments/index.js     | 24 ++++++++++++++++----
 packages/rehype-remove-comments/lib/index.js | 16 ++++++++++---
 packages/rehype-remove-comments/readme.md    | 18 ++++++++++++++-
 packages/rehype-remove-comments/test.js      | 24 ++++++++++++++++++++
 5 files changed, 75 insertions(+), 9 deletions(-)

diff --git a/packages/hast-util-from-string/lib/index.js b/packages/hast-util-from-string/lib/index.js
index 4cd8ad2..5af00c5 100644
--- a/packages/hast-util-from-string/lib/index.js
+++ b/packages/hast-util-from-string/lib/index.js
@@ -16,7 +16,7 @@
  *   Nothing.
  */
 export function fromString(node, value) {
-  const normalized = value === undefined || value === null ? '' : String(value)
+  const normalized = value === null || value === undefined ? '' : String(value)
 
   if ('children' in node) {
     node.children = []
diff --git a/packages/rehype-remove-comments/index.js b/packages/rehype-remove-comments/index.js
index acab358..6d55c8b 100644
--- a/packages/rehype-remove-comments/index.js
+++ b/packages/rehype-remove-comments/index.js
@@ -30,11 +30,26 @@
  *
  * Configuration (TypeScript type).
  *
- * ##### Fields
+ * ###### Fields
  *
- * *   `removeConditional` (`boolean`, default: `false`)
- *     — remove conditional comments (default: `false`); the default is to
- *     leave them
+ * * `removeConditional` (`boolean`, default: `false`)
+ *   — remove conditional comments (default: `false`); the default is to
+ *   leave them
+ * * `test` (`Test`, optional)
+ *   — choose which comments to keep (optional)
+ *
+ * ### `Test`
+ *
+ * Test a comment (TypeScript type).
+ *
+ * ###### Parameters
+ *
+ * * `value` (`string`)
+ *   — comment value
+ *
+ * ###### Returns
+ *
+ * Whether to keep the comment (`boolean`, optional).
  *
  * @example
  *   {}
@@ -44,6 +59,7 @@
 
 /**
  * @typedef {import('./lib/index.js').Options} Options
+ * @typedef {import('./lib/index.js').Test} Test
  */
 
 export {default} from './lib/index.js'
diff --git a/packages/rehype-remove-comments/lib/index.js b/packages/rehype-remove-comments/lib/index.js
index 0916799..33bafdc 100644
--- a/packages/rehype-remove-comments/lib/index.js
+++ b/packages/rehype-remove-comments/lib/index.js
@@ -6,8 +6,17 @@
  * @typedef Options
  *   Configuration.
  * @property {boolean | null | undefined} [removeConditional=false]
- *   Remove conditional comments (default: `false`); the default is to leave
- *   them.
+ *   Remove conditional comments (default: `false`);
+ *   the default is to leave them.
+ * @property {Test | null | undefined} [test]
+ *   Choose which comments to keep.
+ *
+ * @callback Test
+ *   Test a comment.
+ * @param {string} value
+ *   Comment value.
+ * @returns {boolean | null | undefined}
+ *   Whether to keep the comment.
  */
 
 import {isConditionalComment} from 'hast-util-is-conditional-comment'
@@ -38,7 +47,8 @@ export default function rehypeRemoveComments(options) {
       if (
         typeof index === 'number' &&
         parent &&
-        (settings.removeConditional || !isConditionalComment(node))
+        (settings.removeConditional || !isConditionalComment(node)) &&
+        (!settings.test || !settings.test(node.value))
       ) {
         parent.children.splice(index, 1)
         return index
diff --git a/packages/rehype-remove-comments/readme.md b/packages/rehype-remove-comments/readme.md
index 5bf5e04..00e6b03 100644
--- a/packages/rehype-remove-comments/readme.md
+++ b/packages/rehype-remove-comments/readme.md
@@ -21,6 +21,7 @@
 * [API](#api)
   * [`unified().use(rehypeRemoveComments[, options])`](#unifieduserehyperemovecomments-options)
   * [`Options`](#options)
+  * [`Test`](#test)
 * [Example](#example)
 * [Syntax](#syntax)
 * [Syntax tree](#syntax-tree)
@@ -125,11 +126,26 @@ Transform ([`Transformer`](https://github.com/unifiedjs/unified#transformer)).
 
 Configuration (TypeScript type).
 
-##### Fields
+###### Fields
 
 * `removeConditional` (`boolean`, default: `false`)
   — remove conditional comments (default: `false`); the default is to
   leave them
+* `test` (`Test`, optional)
+  — choose which comments to keep (optional)
+
+### `Test`
+
+Test a comment (TypeScript type).
+
+###### Parameters
+
+* `value` (`string`)
+  — comment value
+
+###### Returns
+
+Whether to keep the comment (`boolean`, optional).
 
 ## Example
 
diff --git a/packages/rehype-remove-comments/test.js b/packages/rehype-remove-comments/test.js
index 08f363a..535f07a 100644
--- a/packages/rehype-remove-comments/test.js
+++ b/packages/rehype-remove-comments/test.js
@@ -49,4 +49,28 @@ test('rehype-remove-comments', async function (t) {
       )
     }
   )
+
+  await t.test(
+    'should remove conditional comments w/ `removeConditional`',
+    async function () {
+      assert.deepEqual(
+        rehype()
+          .use(min, {
+            test(value) {
+              return /b/.test(value)
+            }
+          })
+          .runSync(
+            h(undefined, [
+              h('div', [
+                {type: 'comment', value: 'a'},
+                {type: 'comment', value: 'b'},
+                {type: 'comment', value: 'c'}
+              ])
+            ])
+          ),
+        h(undefined, [h('div', [{type: 'comment', value: 'b'}])])
+      )
+    }
+  )
 })